Lift trucks and other industrial vehicles have various drive train arrangements. These drive train arrangements generally include an internal combustion engine, a torque converter, a transmission, a driveshaft, and a drive axle. In some industrial vehicles the transmission, driveshaft, and drive axle are combined into a trans axle. The internal combustion engine and torque converter are usually attached directly to the trans axle. Industrial vehicles without trans axles frequently have drive trains with the internal combustion engine, the transmission, and the axle rigidly attached to each other. Because industrial vehicles such as lift trucks have the drive axle attached rigidly to the frame, both of the above drive train arrangements result in a rigid connection between the engine and the vehicle frame.
A rigid connection between an internal combustion engine in a vehicle frame transfers engine vibrations and noise directly to the frame. Such vibrations in the frame reduce operator comfort and can cause metal fatigue and other problems. Attempts to improve operator comfort by providing enclosed cabs mounted on the vehicle frame by rubber isolation mounts have had limited success. The various controls that are required on industrial vehicles tend to transfer vibration and noise into the enclosed cab. Controls which do not transfer noise and vibration are expensive to manufacture and may not provide the required reliability. Cabs are not used on many industrial vehicles for various reasons. Vibration and noise at the operator's station on vehicles without cabs cause operator discomfort.
Isolation mounting of internal combustion engines reduces noise and vehicle vibration, improves operator comfort, whether the operator is in an enclosed cab or not. Drive trains with isolation mounted engines that have the torque converter and transmission rigidly connected to the engine and employ a driveshaft with universal joints to transfer torque from the transmission to the drive axle are employed in passenger vehicles and highway trucks. The driveshafts in passenger vehicles and highway trucks are generally several feet long. Many industrial vehicles cannot use a long driveshaft with universal joints because it would require an increase in vehicle length. An increase in the length of a lift truck for example, will reduce maneuverability and may make the lift truck unusable in some buildings and in some storage areas. Driveshafts can be shortented to a limited extent. The shorter a driveshaft is, the greater the angular changes to be accommodated by the universal joints. A small increase in the angle at which universal joints operate can result in a substantial decrease in universal joint life.